Quarks and interactions

example: 2 protons collide and a down-antidown quark pair is created, giving a pi-plus meson, a neutron and a proton. with all those quarks knocking around, are there specific rules saying which particles are formed from them? like, what stops there being a pi-zero meson and 2 protons? or any other combinations thereof??

example: 2 protons collide and a down-antidown quark pair is created, giving a pi-plus meson, a neutron and a proton. with all those quarks knocking around, are there specific rules saying which particles are formed from them? like, what stops there being a pi-zero meson and 2 protons? or any other combinations thereof??

I don't know your level, but this can get a bit technical. There is an internal symmetry called "isotopic spin" (In group theory language, it is
SU(2)) that can be used to determine branching ratios like that.
If you are interested, I could relate branching ratios for different final states. You could have [pi+pi-, pi0pi0, pi+pi+, pi+pi0] and two nucleons, each at a specific rate compared to the other 3 three.